Why are the UV coordinates from dupli parent returning black?
Because you are duplicating from verts.

Seems that Blender currently (2.75a) can't inherit coordinates of duplicated objects from the parent only if they are not duplicated from faces.



It would not be tehorically impossible to obtain the behavoiour you need as object mapping should not be strictly related to the way is generated, but for the moment it is. 



The same issue is present with particles:



Note: is not clear why it doesnt work with with grid option enabled...